In a typical sewing machine of the type often referred to a “lockstitch” machine, the to-be-sewn fabric or work-piece is moved beneath a sewing head and is passed over a sewing machine platen positioned directly beneath the sewing head. The platen typically includes an elongated aperture together with a pair of fabric advancing mechanisms positioned on each side of the aperture.
The sewing machine head supports a sewing needle reciprocating and stroke movement mechanism which moves the needle vertically in a repetitive stroke. The needle moves from a raised position above the platen through a downwardly traveling stroke extending into the platen aperture and then returns upwardly to the raised position. This vertical up and down reciprocating motion is repeated as the work-piece or fabric is being moved through the machine.
In a typical sewing machine, two supplies of thread are utilized. The primary supply is housed upon a spool usually supported on an upper surface of the machine. This primary supply of thread is fed to the needle and thus is typically referred to as the “needle” thread. The needle thread is drawn from the primary spool atop the machine and is passed through various guides and tensioners finally being passed through an aperture formed near the pointed bottom end of the needle.
The second supply of thread for the sewing machine is wound upon a smaller spool known as the bobbin which is supported beneath the machine platen. Typically, the bobbin also supports a stitch-locking mechanism which functions to interlock the bobbin thread and the needle thread to form the machine stitching. Proper thread tension for the needle thread and bobbin thread is required for correct functioning of the machine.
In most sewing machines, a mechanism is provided which facilitates winding a quantity of thread onto the bobbin prior to sewing. While certain machines use a separate bobbin winder and bobbin thread supply, most provide a built in bobbin winding mechanism which allows the user to wind a quantity of thread from the main thread spool atop the machine. Thereafter, the thread is cut and the bobbin is positioned beneath the platen. The remaining end of the thread spool is passed through the appropriate guides and tensioners and the aperture in the needle.
Because the bobbin is much smaller than the main spool atop the sewing machine, the amount of thread wound upon the bobbin usually referred to as the “bobbin” thread is substantially less than the supply of needle thread stored in the main spool atop the sewing machine. The smaller amount of bobbin thread wound upon the bobber, causes the bobbin thread supply to be frequently exhausted during sewing. Once the bobbin thread runs out, sewing must be halted and the bobbin changed or reloaded.
The frequent stops during sewing operations required to reload the bobbin thread supply are annoying and vexing to the sewing machine operator. However, perhaps even more annoying is the continued run-out of the sewing machine which occurs prior to the machine operator detecting the exhaustion of bobbin thread. Usually, the machine operator must back up to a point upstream of the bobbin thread run-out occurrence and reposition and restart the stitching operation after replenishing the bobbin supply.
Because of the problems and difficulties associated with bobbin thread supply exhaustion, practitioners in the art have endeavored to provide apparatus which in some manner monitors the supply of thread upon the bobbin and alerts the machine operator to imminent bobbin thread exhaustion. For example, U.S. Pat. No. 3,832,960 issued to Mayer, et al. sets forth a NEEDLE THREAD MONITOR TO AVOID RUN-OUT OF BOBBIN THREAD includes a bobbin winding device having a counting wheel and a bobbin thread counter is provided for winding a bobbin to its maximum capacity with a known supply of bobbin thread. A needle thread counter having a counting wheel is supported upon the machine within the needle thread path. The needle thread counter is set to terminate operation of the stitching mechanism prior to the run-out of the known supply of bobbin thread which has been wound upon the bobbin. A warning mechanism is also utilized to alert the operator to the remaining thread.
U.S. Pat. No. 3,991,692 issued to Papajewski, et al. sets forth a BOBBIN THREAD DEPLETION DETECTOR FOR SEWING MACHINE in which a machine bobbin is provided with a rotation counter utilizing an electronic sensor and cooperating slidable flange secured to the bobbin. When the thread is removed from the bobbin, the slidable end flange will drop from the environment of the sensor producing an inductance change which is detected and which is used to signal imminent thread exhaustion.
U.S. Pat. No. 2,420,275 issued to Winberg sets forth a BOBBIN THREAD CONTROLLED SIGNAL FOR SEWING MACHINES in which a supply of thread upon the bobbin is determined by the sliding position of a bobbin spool portion. The position of the bobbin spool portion is moved under the influence of a spring as the supply of thread is removed from the bobbin. An electrical sensor is provided which responds to the movement of the bobbin portion to trigger an alert.
U.S. Pat. No. 2,647,482 issued to Campbell sets forth a BOBBIN SIGNAL having an electric switch in a circuit utilizing a suitable warning device together with means for operatively connecting the switch to the bobbin holder of a sewing machine such that the presence of bobbin thread on the bobbin maintains the switch in an open condition. When the bobbin thread is nearing depletion, the switch is actuated setting the alarm condition.
U.S. Pat. No. 3,129,680 issued to Doemer sets forth a BOBBIN THREAD DEPLETION DETECTOR FOR SEWING MACHINES which includes a magnetic reed switch supported adjacent the sewing machine bobbin together with a biasing magnet supported in a fixed relation to the switch. A magnetic field produced by the magnet maintains the switch in a closed position. As bobbin thread is depleted, the magnet is moved causing interruption of the switch and alarming the operator or terminating machine operation.
U.S. Pat. No. 3,601,073 issued to Simpson sets forth SEWING MACHINES having a bobbin holder receiving and supporting a bobbin such that the bobbin is moved to a signaling position when little or no thread remains on the bobbin. The bobbin is held in a normal position by the thread upon the bobbin when the thread supply is substantial.
U.S. Pat. No. 4,432,297 issued to Kemmel sets forth a LOW THREAD SUPPLY MONITOR IN A SEWING MACHINE having an optical sensor positioned in association with a rotary hook bobbin case. A pulse transmitter is connected to the machine drive shaft to supply pulses to a control circuit connected to the optical sensor. The control circuit responsive to the pulse activates the optical sensor at the appropriate time for monitoring the thread supply on the bobbin.
While the foregoing described prior art devices have to different extents improved the art, there remains nonetheless a continuing and unresolved need in the art for an effective, low cost and reliable system and apparatus for monitoring the bobbin thread supply in a sewing machine.